Electron tube for high voltages



July 24, 1934. C. REINSCHLD 1,967,537

ELECTRON TUBE FOR HIGH VOLTAGES I I Filed Feb. 13. 1930 @uf MMM/f 57hden/or ye @MMM Hf/Orne y Patented July 24, 1934 1;UNITED-.Sme

ELECTRON -TUBE FOR HYIGH-V-OLTAGES f I f v l i K Carlvlteinschild,.Rahlstedt Vnear Hamburg, Gerf many, assignor to C. H. F. MullerAktiengeselli schaft,` Hamburg, Germany', aA corporation of Germany Y f1 f f Application February y1s, i930, serial No, 428,139 Y In GermanyDecember 24, 1929 l My invention -relates'to' improvements inelectronvtubes for high voltages.

In'order toreduc'e the voltage drop between the cathode and anode'inelectron tubes for high -5voltages, particularly in valve tubes forX-ray systems, and-to prevent deformation of the filament of the glowingcathode by the action of the strong electric field of the anode and thebreakdown ensuing therefrom, it has been proposed to dispose the cathodein the axis of the tube freely relatively to the anode, that is withoutproviding means for protecting the anode in the field, such as screensor collecting devices, and the filament of the cathode has been made inthe form of an jarc the apex of which is located close to the anode, thesaid filament being supported at both ends.

In order to provide a filament of the length necessary for high electronemission, a plurality of arc-shaped filaments have been disposed onebeside the other, or in a cylindrical anode a glowing wire has beenprovided which was supported at suitable points.

In this construction it was not necessary to provide a glowing filamentwhich is particularly stiff. But the number of the points located closeto the anode in such a construction is comparatively small, particularlyif the anode is made with a plane bottom, as is usual in View of themanu- 3@ Vfacture thereof. Therefore the voltage drop is always high.

The object of the present improvements is to reduce the voltage drop intubes having long filaments, and with this object in view my inventionconsists in providing a tube in which the glowing cathode, whichpreferably is in the form of a glowing wire, and which is made stiff bybeing curved, is located in a plane parallel to the opposed surface ofthe anode, which surface is located perpendicularly to the axis of thetube. In this construction the filament of the glowing cathode iscomparatively long, and many points of the lament are located close tothe anode. Therefore the tube has a high emission and a lsmall voltagedrop between anode and cathode. By providing a filament which is madestiff by being curved supporting means are necessary only at few points.Thus the tube is comparatively simple in construction, and yet there isno danger o of break-down by deformation of the glowing filament by theaction of the field of the anode.

For the purpose of explaining the invention two examples embodying thesame have been shown in the accompanying drawing in which the same{a-reference characters have been used in all the views to indicatecorresponding parts. In said drawing,

Fig. 1 is a sectional elevation showing the tube,

Fig. 2 is a detail perspective'view showing a part'of the anode and thecathode of Fig. 1 to an 'B enlarged scale, andI Fig. 3 is a sectionalelevation showing a modification.' i

In the construction shown in Figures 1 and 2 the X-ray tube comprises anenvelope a of glass, a tubular anode b having a plane bottom k disposedperpendicularly to the axis of the tube, and a glowing cathode c. Thecathode consists of a helically wound wire of tungsten or other suitablemetal, bent into the form of a ring or annulus, the said ring beingconnected at both ends to the leading-in wires d and e of the heatingcurrent. The ring is supported by the said leading-in wires f and g andby three additional rods h connected to the wire at suitable points andfixed to a block i of glass supported on the tube in a manner known inthe art.

The plane including the ring c is perpendicular to the axis of the tubeand therefore parallel to the bottom or opposed surface k of the anodeb. The individual coils of the helically wound wire are comparativelysmall, so that the wire c is comparatively stiff.

The distance between the bottom k of the anode b and the glowing cathodec depends on the potential difference for which the tube is designed,and many points of the wire c are located close to the bottom b of theanode, because the wire is bent into a ring having its plane parallel tothe bottom of the anode. Therefore the voltage drop between anode andcathode is small. By providing a helically wound wire the cathode islong, so that the electron emission is high. For example, if theelectron tube is used as a valve tube in an X-ray g5 system and with apotential of 100,000 volts, the voltage drop is on an average reduced by15% as compared to a glowing wire consisting of an arc-shaped wirehaving its apex at the side of the bottom lc of the anode b. By reasonof the stiffness of the helical wire c three additional supports h aresufficient for preventing deformation of the glowing wire between theleading-in wires f and g. Thus the cathode can be manufactured at lowcost.

In the modification shown in Fig. 3 the construction of the cathode c isthe same as that described with reference to Figs. 1 and 2, but theanode is in the form of a hollow body or inverted cup having a closedend m and a cylin- 110 drical side wall n. The anode is made fromtungsten or molybdenum, and its Wall is so thick that it does not allowthe passage of X-rays therethrough. Within the said cup the helicallyWound glowing wire is located which is bent into the form of a ring, andwhich has its plane parallel to the closed end m of the anode.

The said valve tube is contructed in the form of a metal tube, theenvelope consisting of upper and lower portions a of glass and a medianportion o made from chrome-iron alloyv increasing the safety againstbreak-down of the tube. Between the cathode c and the end of the tube,but Within the cup-shaped anode m, Y'n the support of the cathodecarries an insulated plate p of tungsten preventing the passage of lightand X-rays from the anode.

In this construction of the anode the helically wound wire c is not onlyparallel to the opposed surface m of the anode, but it is alsosurrounded at itsside by the anode cylinder n. Thus the number of thepoints of the wire located close to the anode is further increased, andthe loss of voltage is reduced accordingly. Practically all theelectrons must be transmitted from the glowing wire c to the anode m, n.

If desired the chrome iron cylinder o may be reinforced by lead or othermeans adapted to absorb X-rays. The length of the valve tube shown inFig. 3 is reduced in view of the principle of the distribution of thevoltage as compared to a valve tube comprising a glass envelope.Ordinarily Rntgen apparatus require much space, and they cannot easilybe operated by reason of the extended insulation needed in theapparatus. Therefore the reduction of the length caused in my improvedsystem Vis important.

In the valve tubes described above the glowing filament c may also bebent into zigzag form, consisting of a plurality of loops or rings whichare located Within a plane parallel to the bottom of the anode. l

I claim:

A high-voltage electron-discharge tube comprising an envelope, a coiledconcentrated lamentary cathode in said envelope adapted to emitelectrons, an anode in said envelope having a substantially fiat surfacelying in a plane perpendicular to the axis of the tube, said cathodebeing in the form of a loop lying in a plane closely spaced from andparallel with said surface of the anode, and means supporting thecathode intermediate the ends thereof.

CARL REINSCHILD,

